E. Tóth-Kádár

Structure and properties of fine-grained electrodeposited nickel

Abstract The structure and some physical properties (electrical resistivity and its temperature coefficient, thermoelectric power, Curie temperature) were investigated for electrodeposited Ni foils. The values of these parameters deviated from those of equilibrium, coarse-grained physical properties could be ascribed to the nanocrystalline structure of the deposits which was verified by transmission electron microscopy and X-ray diffraction.

Microstructure and electrical transport properties of pulse-plated nanocrystalline nickel electrodeposits

Abstract The microstructure and the electrical transport properties (the electrical resistivity, its temperature coefficient and the thermoelectric power) were investigated for pulse-plated nanocrystalline nickel electrodeposits. Transmission and scanning electron microscopy were used to study the microstructure (grain size and lattice defects) and the surface morphology respectively. The samples were prepared from the same bath as used previously for d.c. plating and the deposition current density was constant, in most cases i dep = 20 A dm −2 . In a given series, the pulse length t on was kept constant at 0.001, 0.01, 0.1, 1 or 10 s and the separation between pulses t off was varied from 0.001 s to 10 s. Systematic variations of the electrical transport parameters with t on and t off were observed, which we attempt to explain in terms of the periodic variation due to pulse-plating of the local Ni 2+ concentration at the cathode-electrolyte interface.

Microstructure and growth of electrodeposited nanocrystalline nickel foils

In the present work, the structure of electrodeposited pure Ni foils has been investigated by X-ray diffractometry, transmission electron microscopy and by measuring their electrical transport properties. It was found that the as-deposited Ni foils have a nanocrystalline structure covered by a thin amorphous Ni layer on the substrate side: the growth of the electrodeposited foils starts in amorphous form followed by nanocrystalline layers. To explain the formation of the amorphous Ni layer, it is supposed that foreign atoms are incorporated into the nucleating Ni films.

Magnetic and electrical transport properties of electrodeposited Ni-Cu alloys and Ni81Cu19/Cu multilayers

Electrodeposited Ni-Cu alloys and nanoscale Ni-Cu/Cu multilayers were produced by direct-current plating and pulse-plating, respectively. The room-temperature electrical resistivity and thermopower as well as the Curie temperature for the Ni-Cu electrodeposits were in good agreement with relevant data reported for metallurgically processed Ni-Cu alloys. The same parameters were investigated also for the multilayers as a function of the constituent magnetic and non-magnetic layer thicknesses. The electrical resistivity of the multilayers was much larger than calculated for a parallel resistance model and their thermopower was more negative than expected on the basis of a volume average model, by using bulk values of both parameters for the sublayer materials. These differences were ascribed to surface scattering processes which can be significant in nanoscale multilayer structures.

Magnetization and NMR study of amorphous Ni-P alloys in the paramagnetic concetration range

Abstract The temperature- and field-dependence of magnetization, and the 31 P NMR linewidth and Knight shift of some amorphous Ni 100− x P x alloys with 18⩽ x ⩽ 22 prepared by melt-quenching and electrodeposition were studied below room temperature. Although all the alloys investigated contain magnetic inhomogeneities, the amount and nature of which depend on impurities and on the details of sample preparation, it could be established that the amorphous matrix of Ni 100− x P x alloys with x ⩾ 18 exhibit Pauli paramagnetism and the Pauli susceptibility was found to decrease rapidly with P content. From the results, a similarity of the electronic structure and the short-range order in amorphous Ni-P alloys and in the crystalline Ni 3 P compound is deduced.

A cross-sectional high-resolution transmission electron microscopy study of electrodeposited Ni–Cu/Cu multilayers

Abstract This work is an extension of our previous structural study performed by conventional transmission electron microscopy (TEM) on electrodeposited Ni–Cu/Cu multilayers exhibiting giant magnetoresistance (GMR). It could be established from the present atomic-resolution structural studies that (i) the layered structure found by conventional TEM to be flat and smooth shows an interface roughness spread over a few atomic monolayers; (ii) the atomic planes cross, in most cases, continuously the Ni–Cu/Cu interface, i.e., forming a coherent superlattice; (iii) the atomic planes exhibit a periodic distortion due to the unrelaxed strain induced by the lattice mismatch between the magnetic and non-magnetic constituent layers.

Preparation, structure, magnetic, and magnetotransport properties of electrodeposited Co(Ru)/Ru multilayers

It is demonstrated that Co(Ru)/Ru multilayers with a hexagonal close-packed structure can be produced by electrodeposition. For appropriate layer thicknesses, clear giant magnetoresistance (GMR) behavior has been found. The observed GMR is very small (less than 0.1% for 8 kOe at room temperature) but not smaller than the GMR of Co/Ru multilayers prepared previously by high-vacuum methods. It is argued that neither structural imperfection of the multilayers nor chemical intermixing at the interfaces can be the main reason for the small GMR observed in the Co-Ru system for any preparation technique. It is suggested that the strongly reduced spin-dependent scattering characteristics of the interfacial Co-Ru alloys, which was described in a previous paper, might explain the low GMR of Co/Ru multilayers.

TEM and XRD study of the microstructure of nanocrystalline Ni and Cu prepared by severe plastic deformation and electrodeposition

Abstract It has been shown recently that techniques such as severe plastic deformation and electrodeposition are able to yield porosity free massive nanocrystalline metal samples in a single-step process. In the present work, a comparison of the microstructures is made for nc nanocrystalline Ni and Cu samples prepared in the form of disk-shaped foils by these two techniques.

Hydrogen-induced phase-separation in the amorphous Ni-Zr system

Abstract It is found that the magnetic state of the amorphous Ni 60 Zr 40 samples changes from paramagnetic to superparamagnetic upon hydriding. The density and the size of the magnetic clusters induced by the hydriding process was determined by magnetic and scanning transmission electron microscopic (STEM) measurements.

Hydrogen Absorption and Hydrogen-Induced Phase-Separation in Amorphous Zr50Ni50−xCux Alloys

The hydrogen absorption from the gas phase was investigated for melt-quenched ZrsoNiso.xCu, (0 < x < 25) amorphous alloys by weighing, by thermoelectric power (TEP) and magnetization measurements and by electron microscopy. A strongly nonmonotonous behaviour been observed, both as a function of the charging time and the Cu-content, for several materials characteristics and also for the nature of the hydrogeninduced phase-separation.